Block copolymers in general are known to those skilled in the art, and have been made using many different types of polymers for the blocks. Block copolymers are often made in the hope of obtaining a combination of the desirable properties characteristic of each block, but the outcome is usually not predictable. Some aramid block copolymers have been previously reported.
A. Ya. Yakubovich, et al., Vysokomol. Soyed., vol. A14, p. 1838-1842 (1972), report the synthesis of various aramid block copolymers. It is believed all of these blocks remain flexible whether drawn or not. Most of these block copolymers were made by preforming both types of blocks and then reacting to combine them into a block copolymer.
In a series of papers, W. R. Krigbaum and coworkers investigated the synthesis and properties of several aramid block copolymers. All of these block copolymer contained one type of block that was always flexible, and another type of block that was rigid in solution and/or without drawing. The first of these papers [J. Polym. Sci., Part A, Polym. Chem., vol. 25, p. 653-667 (1987)] describes the synthesis of the polymers, and in all of the methods used, the authors report varying amounts of homopolymer due to inability to completely couple the blocks into a block copolymer. The second [J. Polym. Sci., Part B, Polym. Phy., vol. 25, p. 1043-1055 (1987)] and third [Polym. J., vol. 20, p. 83-91 (1988)] papers describe properties of these aramid block copolymers. The fourth paper [J. Polym. Sci., Part C, Polym. Lett., vol. 27 p. 59-63 (1989)] reports an improved synthesis using a phosphorylation reaction, which gives more efficient coupling of the aramid blocks.
Japanese Patent Application 51/041097 describes the preparation of aramid block copolymers. None of these is believed to contain an aramid block that contains flexible chains in solution and the undrawn state, that become rigid upon drawing. The polymers are reported to be made by preforming one block as a suspension of a solid in liquid, and then adding the monomers that form the second block.